This invention relates to a radial-flow pump, and especially a coolant pump for an internal combustion engine, comprising an impeller provided with vanes and a directing device including at least one temperature- and/or speed-sensitive element for temperature-dependent control of the coolant flow, at least one impeller vane and/or the directing device being configured as a speed-sensitive element.
Coolant pumps for use with engines of large passenger cars are often required to handle considerable flow volumes even at low engine speeds. As a consequence extremely large volumes are delivered at maximum speed, which in turn will lead to unduly high pressures in the coolant circulation system. Short circuits to reduce the coolant volume passing through the engine cooling system must have large cross-sections and will inevitably result in power losses.
Publication DE 37 09 231 A1 describes an impeller made of an extendible elastic material, which is configured such that the impeller diameter will increase with an increase in centrifugal force acting on the impeller vanes as the impeller picks up rotational speed. In this way the output will be increased.
In DE 44 24 996 A1 a centrifugal pump with flexible impeller vanes is disclosed. When the synchronous motor starts against the given sense of rotation the impeller vanes are extended in radial length by at least two percent, which will considerably increase water resistance and brake the motor. Due to the tendency of the single-phase synchronous motor to oscillate during start-up and the preferred direction defined by the impeller, the motor is forced to start with the proper direction of rotation.
DE 30 22 241 A1 describes a coolant pump configured as a radial-flow pump with a control device, which has a bladed impeller whose vanes are curved in a single direction. The vanes are configured as bi-metallic elements where the component with the higher thermal expansion coefficient is placed on the side of the vane facing the centre of curvature. Under the influence of the coolant temperature and/or the speed of the impeller the curvature of the vanes will change so that with an increase in speed and/or temperature the smallest distance between two adjacent vanes will increase and the throttling of the coolant flow effected by the curvature of the vanes will be reduced accordingly. In the instance of higher rotational speeds a higher throughput may thus be obtained.
A centrifugal pump is also presented in DE 196 54 092 C2, where the impeller vanes are subject to temperature-dependent deformations. An impeller with thermally variable vanes is disclosed in JP 59-70898 A.
DE 42 00 507 A1 describes a variable turbo-machine whose impeller is adjusted to the flow volume by varying the impeller width via an impeller plate consisting of a disk with vane-shaped slits through which the vanes project. The spiral casing may also be varied either via the spiral width by means of a variable flat spiral spring or via the spiral breadth by means of a spiral plunger matching the spiral form.
Another centrifugal pump with variable vanes is disclosed in JP 60-159399 A.
It is an object of the invention to avoid the above disadvantages and to improve the efficiency of a radial-flow pump.
In accordance with the invention this object is achieved by providing that the impeller vanes be elastically deformable by Coriolis forces of the coolant flow, discharge angles which are preferably defined between impeller vanes and impeller tangential planes, decreasing with an increase in speed.
Preferably it is provided that the impeller vanes be configured as flexible elements made of elastic material, preferably sheet steel. At low speeds the pressures exerted on the impeller vanes are low; the delivered flow volume is the same as in the case of rigid vanes. At high speeds, however, the Coriolis forces of the coolant flow will cause a deformation of the blades resulting in smaller discharge angles and thus a reduced flow volume. This is due to the fact that a deformation of the vanes effected by the Coriolis forces will cause the discharge angles defined between the impeller vanes and the impeller tangential planes to decrease with increasing speed. Compared with rigid impeller vanes the flexible vanes are flatter and thinner. The efficiency of flexible vanes is significantly higher than that of rigid vanes, while throttle losses will be avoided.
According to a preferred variant of the invention the impeller vanes are configured at least partially as a bimetallic element. As a consequence they will be deformable by changes in coolant temperature, discharge angles which are preferably defined between impeller vanes and impeller tangential planes increasing with an increase in temperature. This will permit the flow volume to be controlled by means of the coolant temperature. Depending on the desired delivery characteristic the flow volume may deviate in either direction from the characteristic obtained with rigid impeller vanes.
Maximum deformation of the impeller vanes is limited by the use of supporting vanes, i.e., preferably at least in the direction of decreasing discharge angles, the impeller vanes being preferably provided with one supporting vane each. In addition to, or instead of the supporting vanes it may be provided that the impeller vanes be connected to each other by a synchronizing ring. This ring will effect constant parallel alignment of the impeller vanes and prevent bending or displacement of individual vanes. The synchronizing ring further prevents undue excitation of vibrations of individual impeller vanes. If the synchronizing ring is employed together with the supporting vanes, it should preferably be positioned outside of the supporting vanes in radial direction.
Special preference is given to a variant of the invention in which it is proposed that each impeller vane turn about an axle held on the impeller, the axles preferably being arranged in a circle concentric with the impeller axis, and that the impeller vanes be loaded by at least one spring element in the direction of an initial position defining a maximum discharge angle. The impeller vanes may consist of a non-flexible or rigid material. In order to promptly obtain a stable operating position of the impeller vanes it will be of advantage if the impeller vanes are supported against the impeller by means of at least one damping element. In this context each impeller vane may be acted upon by a spring element and/or damping element inside the circle of vane axles. Alternatively, the spring element and/or damping element could act on the synchronizing ring connected to the impeller vanes.
The impeller vanes may be made at least partially from sheet steel or plastic material.
In further development of the invention the proposal is put forward that the directing device, which is preferably constituted by a spiral casing, include at least one bimetallic element, preferably in the shape of a guide vane. The bi-metallic guide vane may change its shape due to temperature changes between a first position for minimum spiral cross-section and a second position for maximum spiral cross-section, the spiral cross-section controlled by the guide vane preferably increasing with an increase in temperature.
To permit external control of the flow volume handled by the radial-flow pump, it will be a special advantage if the temperature-sensitive element can be heated by means of a heating device.